Recently, in the middle of rising of a market of cellular phones applied with the third generation system superior in transmission characteristics to the second generation system according to advance of multimedia application of communication, further cost reduction, size reduction, and lower power consumption are strongly desired in development of the cellular phone. WCDMA (Wide band CDMA) system, one system for the mobile phone of the third generation is specified by 3GPP.
According to a document “3GPP TS 25.101 Release 1999” (Non-Patent Document 1), bands I to II are allocated as UMTS (Universal Mobile Telecommunications System) frequency band. In a document “3GPP TS 25.101 Release5” (Non-Patent Document 2), band III is newly added, and since bands II and III use GSM band, Narrow Band Blocking specification that specifies GSM blocker is newly added. Currently, in the latest specification “3GPP TS 25.101 Release6” (Non-Patent Document 3), bands I to VI are specified and the specifications of the bands II to V define the Narrow Band Blocking.
Currently, a WCDMA-compliant cellular phone is generally compliant to band I and Narrow Band Blocking is not considered. And as its signal receiving system, a direct conversion system that directly converts a received signal from a wireless frequency band to a baseband frequency band is predominant. Generally, a blocker in the signal of the baseband frequency band is removed by a low-pass filter and only a signal component in a wanted band is extracted.
As a conventional art, regarding a filter in a receiving circuit which allows transmission and reception of multi-band wireless signals, an approach performing switching among a plurality of filters to extract only signal components in a wanted bandwidth is disclosed in Japanese Patent Laid-Open Publication No. 2004-32390 (Patent Document 1).
Since Patent Document 1 shows a configuration that restricting a high frequency signal bandwidth inputted from an antenna end to a wanted signal bandwidth by performing switching of band pass filters, it does not take into consideration the Narrow Band Blocking.